1. Field of the Invention
The present invention relates to a communication abnormality detecting/coping device and a vacuum pump remote monitor control device, and more particularly to a communication abnormality detecting/coping device and a vacuum pump remote monitor control device, which are capable of detecting the presence/absence of an abnormality in data communication and reducing an influence of the abnormality on a system device when detecting the abnormality.
2. Description of the Related Art
FIG. 3 is a diagram showing the entire structure of a magnetic floatation type turbo-molecular pump 10. Referring to FIG. 3, a rotor 1 is axially floated by an axial electromagnet 3, and radial position control thereof is conducted by radial electromagnets 5A and 5B. Then, the rotor 1 is rotated by a motor 7. A plurality of rotating blades 9 are axially formed in the rotor 1. A plurality of fixed blades 11 are disposed at the rotating blades with a gap therebetween. One ends of the fixed blades 11 are supported between a plurality of fixed wing spacers 13 which are stacked one on another.
In the turbo-molecular pump 10 thus structured, gas molecules are struck by the rotating blades 9 during its rotation so as to be moved axially, thereby exhausting a gas. The turbo-molecular pump 10 of this type is, for example, used to exhaust the gas from a chamber of an etching device for manufacturing semiconductor (hereinafter referred to as "system device 30"). A gas is always supplied to the chamber to process the semiconductor, and the supplied gas is exhausted by the turbo-molecular pump 10.
In the case where the turbo-molecular pump 10 is controlled by the system device 30, on/off signals using a relay have been employed as input/output signals from/to the turbo-molecular pump 10 up to now.
However, in the case where the relay is used, multiple wirings are arranged to cause an increase in cost and an increase in size. Also, there arises such a problem that analog information of r.p.m. or the like cannot be inputted or outputted.
To cope with the above problem, serial communication control using an RS 232 cable 21 or the like is recently increasingly implemented as shown in FIG. 4. Referring to FIG. 4, the turbo-molecular pump 10 is connected to a bus 25 through a drive circuit 23. The bus 25 is connected with switches such as a stop switch 29 or a start switch 31 through a switch I/F circuit 27.
The bus 25 is connected with a liquid crystal display 33. The bus 25 is also connected with a communication circuit 35 and the system device 30 through the RS232 cable 21. A turbo-molecular pump control device 20 enclosed by a dotted line in FIG. 4 is thus formed with the driver circuit 23, the switch I/F circuit 27, the liquid crystal display 33, the communication circuit 35, a CPU 37 and so on.
By the way, in a conventional case where data communication is conducted between the turbo-molecular pump control device 20 and the system device 30 through the RS232 cable 21 or the like, there may arise the following problems.
FIG. 5 illustrates data communication between the turbo-molecular pump control device 20 and the system device 30. In FIG. 5, data communication in a normal operation is shown. For example, a command 41 such as a start command is transmitted to the turbo-molecular pump control device 20 from the system device 30. The turbo-molecular pump control device 20 returns an acknowledgement signal 43 (hereinafter referred to as "ACK 43") indicative of the reception of the command 41 to the system device 30 and simultaneously starts the turbo-molecular pump 10.
Then, in the case where, for example, r.p.m. data is required in the system device 30, a data request signal 45 is transmitted to the turbo-molecular pump control device 20 by the system device 30. The turbo-molecular pump control device 20 transmits r.p.m. data 47 to the system device 30 in response to the data request signal 45. The system device 30 transmits an ACK 49 which is an acknowledgement signal indicative of the reception of the r.p.m. data 47 to the turbo-molecular pump control device 20.
Thereafter, in the case where a trouble (program runaway) on the part of the system device 30, the disconnection of the cable, falling-out of a connector or the like occurs while the turbo-molecular pump 10 is rotating, communication is hung up. In this situation, because the turbo-molecular pump control device 20 is of a slave, it cannot acknowledge the communication state with the system device 30 which is of a master. As a result, even in the case where the turbo-molecular pump 10 must stop, it continues to rotate, and an energy is unnecessarily consumed.
Also, depending on the operating state, there is a fear that a trouble may be caused in a process on the system device 30 side by stoppage of the turbo-molecular pump 10 immediately after the disenablement of the data communication.